M2 Jet Drive Won't Fire Up

[scarfie]

Man...back to the diagnostics AGAIN. I'll give a run down of the problem and what we've fixed/replaced so far. Maybe there are some ideas out there of further diagnostics we can do.

First off, the engine block is new. Put it in last summer and it ran like a top. We're just past the break-in period of ten hours. Didn't check the compression cause the damn thing is brand new.

Plugs are sparking fine. Just put in a new starter cause the old one seized up. Just put in a new oil pump cause the old one was getting squirrely and I don't want to throw another rod through the block.

Now the problem. I fired up the motor on the hose last weekend for the first time this season. It took two turns of the ignition and cranked right up. I delightedly dropped the boat in the water, fired it up again, got 20 feet from the dock, gave it some throttle and it stalled out. Haven't been able to start it since.

The voltage to the fuel pump is intermittant. Sometimes it's there and the fuel pump works fine, sometimes there is no voltage to the fuel pump. Seems there may be a short in the ignition harness (which I already have on order cause I suspected it had a short).

Thing is, we were able to try to pressurize the fuel system when we had a good connection to the fuel pump. It just won't go. Doesn't seem like there is any gas getting through the system.

Any ideas on what I can check next to diagnose?

Thanks!

 

[wayne99]

Im going to say you have some type of fuel issue.

 

[rookie101]

More than one......

Have you checked power to both the fuel pumps? You have two electric pumps on your engine. One low pressure that is external, and one high pressure that sits in the vapor separator.

The easiest check if you have a fuel pressure tester is to check at the thread on test port. You should get between 34 and 36 psi at the fuel rail. If you are, the fuel pumps are working and the problem lies somewhere else.

Aaron :cheers:

 

[scarfie]

The one we were checking was in the vapor seperator. I wasn't aware of the low pressure external pump. I pulled the drain plug at the bottom of the vapor seperator and only an ounce or so of fuel drained out. Last summer when I drained it, it was more like a quart or so. Sounds like checking the other pump is the next place to look.

I'll take a look at the manual and give it a try sometime this week. Thanks for the replies.

 

[rookie101]

Direction of flow.....

If there is no fuel in the vapor separator the high pressure pump cant draw fuel on its own.

The flow of fuel on your engine is : from the fuel tank to the low pressure electric fuel pump, to the engine driven pulse pump, to the fuel/water separator, then to the vapor separator.

If you have the Mercury manual there is a diagram of the fuel flow on page 3D-19


Aaron:cheers:

 

[scarfie]

I think I'll rebuild the engine driven pulse pump...the diaphragm kit is less than $20.

Can you give me a little more specifics on testing the low pressure pump?

if you have a fuel pressure tester is to check at the thread on test port

Where is the test port?

 

[rookie101]

Pressure....

Don't worry about the test port as it is for the high pressure pump. To check the low pressure pump, make sure it is getting power, then just put a pressure gauge in the out hose. The spec from Mercury is 2-5 psi. The spec for the pulse pump is minimum 1 psi while cranking.


Aaron:cheers:

 

[scarfie]

Found the problem...fuel pressure was fine on the low pressure side. Took the inlet hose off the vapor seperator and got a shirt full of fuel. Had to take the vapor seperator off and take it apart.

There is a float that blocks off the inlet when the seperator is full. It was stuck in the floating position, closing off the fuel inlet. Felt like I was fixing the toilet.

While it was apart, cleaned the final filter and bench tested the internal fuel pump. It was all good.

Got it all backk together and it fired up on the first try! Woo-hoo here comes summer.

Thanks for the help!